In printing technology and, in particular in digital multi-color printing technology, it is known to exactly align sheet-shaped substrates, before they are being printed, with respect to their position in advance direction and their position transverse to advance direction, and to align them in view of potential skewing. A device and a method for the alignment of sheet-shaped substrates are known, for example, from document U.S. Pat. No. 6,663,103 B2. The device described therein comprises several pairs of rollers on various axles that are parallel to each other and at a distance from each other in the advance direction of the sheets, said pairs of rollers performing different alignment operations. In this device and method, the technical problem arises that, because the axles of the pairs of rollers that are parallel to each other and at a distance from each other in advance direction of the sheets, the devices takes up a large amount of space. Furthermore, when a transfer takes place between the pairs of rollers that are at a distance from each other in advance direction, an alignment error—that had already been corrected previously—may be introduced.
In addition, a method and a device for the alignment of sheet-shaped substrates in a printing machine is known from document DE 691 24 755 T2. In the device described therein, two pairs of transport rollers, which are spaced apart in a direction transverse to the advance direction of the sheet, are provided. Each of the pairs of transport rollers comprises one driving roller and one counter-pressure roller, both being arranged on a common carriage. The drive motors for the driving rollers are also located on the common carriage. In order to achieve a correction of the skew of a sheet, the driving rollers may be actuated, for example, at different rotational speeds and/or at different points in time. In order to achieve a correction of a sheet position transverse to its advance direction, the aforementioned carriage, which supports the pairs of transport rollers as well as the drive motors for the driving rollers, can be shifted in transverse direction. To achieve this, the carriage is located on a carriage guide so as to be transversely shiftable, and a motor is provided which controls the shift of the carriage along the guide. The motor must be designed in a relatively strong manner because it needs to move the entire carriage, including the drive motors for the driving rollers. In addition, the entire assemblage of the carriage must be designed in highly robust manner in order to prevent that vibrations occurring as a result of the shifting of the carriage will impair the sheet alignment and/or the integrity of the carriage.